Effects Of Livestock Wastewater Treatment On The Physiological Characteristics Of Phragmites Australis

The plant metabolism systems were balanced when they were growing in a benign environment. When living in a bad environment plants would start their protecting system to get through the difficulties. But the effects of self-protecting were limited, and when the hard time lasted too long or stress intensity exceeded the extent that plants could endure, the plants' defense capability would get weak and the plants metabolism systems might get hurt. Research on the plants' stress was one of the studying hotspots, and the untreated livestock wastewater would be the eutrophic stress to the plants. In this paper, we studied the effects of livestock wastewater treatment on the physiological characteristics of Phragmites australis, using simulated experiment of natural condition under stress of two concentration of livestock wastewater. The aim was to find out the mechanism of the eutrophic stress and to provide the theoretical basis for further research on the decontamination of wastewater with constructed wetland growing plants. The results were as follows:(1) The results show that the effects of two concentration of livestock wastewater stress on the physiological characteristics of Phragmites australis are similar, but different on the stress strength. The effects of each physiological index under long-term continuous stress of high concentration of raw livestock wastewater were greater than that of mid-concentration of livestock wastewater. Other physiological indexes of Phragmites australis growing in constructed wetland were obviously higher than that of Phragmites australis growing in Fenjiang River under natural conditions, except for the content of malondialdehyde (MDA) and the activities of superoxide dismutase (SOD).(2) The Activities of superoxide dismutase (SOD) increased obviously under the stress of livestock wastewater. The activities of peroxidase (POD) decreased in the first three days and then reached almost the same activities at the end of the treatment when compared with control, and the activities of catalase (CAT) gradually decreased all the time. The variation tendency of the activities of POD showed that Phragmites australis were greatly hurt at the beginning but with the stress time went on the Phragmites australis gradually adapted to the livestock wastewater. The obviously increased activities of SOD indicated that the body of Phragmites australis produced a great deal of superoxide anion radical (O(?), and it would inevitably produce H₂O₂ when it alleviated the harm brought by O(?), while the variation trend of the activities of POD and CAT showed that POD and CAT did not take effect on getting rid of H₂O₂ produced by O(?) from the increased activities of SOD, and the stress could not activate the enzymes of antioxidative system. So it could be inferred that Phragmites australis have another protection mechanism to get rid of the harm brought by accumulation of H₂O₂. This protection mechanism probably was relevant to some other non-enzyme protection systems clearing off the active oxide.(3) The content of chlorophyll decreased gradually, while the value of chlorophyll a/b presented an increasing tendency under the stress of livestock wastewaters, it was just opposite to the content of chlorophyll. The decreased content of chlorophyll indicated that photosynthesis of leaves of Phragmites australis was partly affected, and the leaves of Phragmites australis had an indication of growing old, but it was not greatly. The cause of the increased value of chlorophyll a/b was that the content of chlorophyll b decreased more quickly than that of chlorophyll a during the stress time, this showed that chlorophyll a/b value was affected mainly by content of chlorophyll b.(4) The root activities of Phragmites australis obviously increased, the content of praline (Pro) kept steadily at a lower level after rapidly decreased, the content of MDA gradually decreased, and the electrolyte leakage was weak during the stress time. Root activity was a very important physiological index of plants, and the increased root activities of Phragmites australis contributed to the harm resistibility and helped to increase anti-oxidative abilities from the livestock wastewater stress. It was a positive response to the stress. High accumulation of root activities lasting nearly a month under the stress indicated that some specifically adaptabilities were formed in Phragmites australis. Reduced content of proline indicated that Phragmites australis could not able to rely on the accumulation of praline to enhance anti-adversity abilities under the stress of livestock wastewater. In other words, the damage was strengthened. MDA was an important product of the peroxidation of cell membrane lipid. The gradually reduced MDA showed that the cell membrane system of Phragmites australis didn't get strong damaged under the stress of livestock wastewater, and the peroxidation of cell membrane lipid was weak. The variation of the permeability of cell membrane was very complicated. The permeability of cell membrane decreased and increased again and again during the treatment under high concentration of livestock wastewater stress, while under the stress of mid-concentration of livestock wastewater, the permeability of cell membrane decreased at the beginning and then increased but still lower than control at the end of the treatment(P＜0.01).(5) The results of the variation of physiological characteristics of Phragmites australis under the stress of livestock wastewater showed that the stress of high concentration and mid-concentration livestock wastewater had lower effects on the growing condition of Phragmites australis, and Phragmites australis showed stronger stress resistances and tolerances. The effects of the growing of Phragmites australis was still very weak under nearly a month's stress of raw livestock wastewater, so Phragmites australis can be applied to biodegradation of any concentration livestock wastewater and can be used as one of the wetland plants treating livestock wastewater. Given the experiences that Phragmites austraIis had very excellent purifying abilities and had been triumphantly applied to the treatment of city wastewater, it would enormously relieve the contradiction between the development of livestock breeding and environment contamination if it would be used to the treatment of our nation's livestock breeding wastewater.